The present invention relates to a motor vehicle seat designed to receive a safety belt and comprising a seat part and a back part on either side of a hinging zone, each of the said parts having a frame with two arms terminating at the hinging zone, the two arms forming respectively seat side members and back upright members.
Hinging mechanisms of motor vehicle seats permitting adjustment of the slope of the back part are not designed to withstand large forces transmitted by the safety belts in the case of an accident. Transmission of these forces would necessitate considerable overdimensioning of these mechanisms.
That is why, generally, the high anchorage point of the belt is not fixed to the seat but to the vehicle body, generally arranged at floor level by the lateral columns, called pillars, of the body structure. This layout requires arrangement of the fixing points and separate, successive installation of the seats and belts, which increases the assembly times on the assembly line.
It is even more difficult to choose the high anchorage point for the removable seats of vehicles of the people-carrier or utility type.
Moreover, the offset position of a high anchorage point fixed on the back part relative to the axial plane of the seat promotes deformation by twisting of the said back part, greatly reducing its capacity for absorbing a tensile stress on the anchorage point of the safety belt.
The present invention relates to a seat in which the force transmitted mainly by a single upright member of the back part receiving the high anchorage of the safety belt is distributed equally on the two seat side members of the seat to withstand dynamic forces of the order of 400 decanewton-meter; owing to this arrangement, the safety belts can be installed forming an integral subassembly of the seat.
According to the invention, a motor vehicle seat designed to receive a safety belt and comprising a seat part and a back part on either side of a hinging zone, each of the said parts having a frame with two arms terminating at the hinging zone, the two arms forming respectively seat side members and back upright members, is characterized in that the ends of the two arms of one of the said parts and the ends of the two arms of the other part are each mounted with rotation by means of a pivot in a bearing, the pivot being carried by one part and the bearing by the other part, a means of absorbing energy being provided between at least one pivot and its corresponding bearing.
Advantageously, a stiffening crosspiece is arranged between the pivots carried by the ends of the arm of the said one of the parts.
Preferably, the energy absorbing means has at least one elastic element.
Advantageously, the energy absorbing means has two elastic elements that are designed to come into operation, one instantly without any play, and the other deferred after a travel determined by an amount of play.
Preferably, the elastic means whose operation is deferred is provided with a certain amount of play in one direction and a different amount of play in the other direction.
Advantageously, as the crosspiece is tubular, the energy absorbing means is arranged inside the said crosspiece.
Preferably, the absorbing means has at least one torsion bar with one of its ends fixed in one of the bearings and connected by a coupling block to the tubular crosspiece.
Advantageously, the tubular crosspiece with overall cylindrical shape has at least one helical rail that cooperates with at least one corresponding groove arranged on the coupling block, and the torsion bar that passes through this block with a non-circular cross-section blocks any relative rotary movement between block and bar, but permits their relative free sliding.
Preferably, the block has a tapped through-hole, and a screw parallel to the axis, free to rotate but blocked in translation and accessible from the outside by at least one of its ends constitutes a means of so-called continuous fine adjustment of the slope of the back part.
Advantageously, the said screw is able to be operated by one and/or the other of its ends.
Preferably, the torsion bar of non-circular cross-section has one of its ends fixed in a bearing, and is engaged by its other end in a housing provided in the other bearing with a similar shape but of larger dimensions so as to block that other end in rotation only beyond a certain angle of rotation.
Advantageously, the torsion bar of square cross-section has its other end engaged in a housing with a cross-section delimited by two squares centred on the axis and with an angular offset with a predetermined angle of displacement, the rotational displacement of each vertex of the bar""s cross-section being delimited by two flat bearing surfaces connected following a circular arc with diameter at least equal to the diagonal of the square of the bar""s cross-section.
Preferably, a difference provided between the distances separating the coupling block of the two ends of the bar is utilized as a means of acting upon the distribution of the stresses applied in case of impacts on the seat side members.
Advantageously, sleeves inserted in the tubular crosspiece or fitted on the torsion bar limit the axial displacements of the coupling block.
Preferably, sleeves fitted on the torsion bar provide guidance of the control rod of the block.
Advantageously, the said at least one helical rail extends over a fraction of the length of the crosspiece.
Preferably, one of the ends of the said rail is configured as a stop that limits the axial displacement of the block, whereas the other end is configured to facilitate the introduction of the block.
Advantageously, a device for manual selection of the angle of slope of the back part is interposed between at least one of the bearings carrying the said one of the parts and the end of the corresponding arm of the said other part.
Preferably, the device for selecting the angle of slope of the back part having a limited number of positions for angular blocking, the means for fine adjustment is designed for continuous coverage of a range of adjustment over an angular extent greater than the difference separating two successive positions for angular blocking of the selecting device.
Advantageously, the, or each, energy absorbing means is an elastic element that is designed to undergo a permanent deformation in case of impact.
Preferably, the elastic element is divided into at least two parts, one at least of these parts having been treated to modify its elastic limit.
Advantageously, the ends of the two upright members of the back part being joined together solidly by the stiffening crosspiece whose ends, extending outside of the upright members of the back part, form hinging pivots in two bearings fitted on said ends, each of these bearings has, in relief on its external face, a blocking means that is able to cooperate by complementarity of shape with a receiving means provided in the hinging zone of the corresponding seat side member.